Wayan Suparta has used GPS measurements of atmospheric water vapor to predict when lightning is most likely to strike in Malaysia, a region that experiences large lightning storms throughout the Northeast monsoon season (November-March).

Making the Measurements

Suparta took atmospheric water vapor data as measured by GPS, and compared them with other meteorological variables and lightning strikes in one-minute intervals. He found that atmospheric water vapor increased with the first cloud-to-cloud lightning and prior to any cloud-to-ground lightning. Water vapor stayed high throughout the lightning event, and fell as the event ended.

He made his measurements in November of 2009, which is during the Northeast monsoon season in Malaysia, using a combination of data from a GPS station at his university in Bangi, Malaysia, meteorological equipment that measures temperature, air pressure and relative humidity, and eight Lightning Monitor and Alert Interferometry Radios (Surveillance et Alerte Foudre par Interférometrie Radioélectriques (SAFIRs)) in the vicinity of the GPS station. SAFIRs can detect both cloud-to-cloud and cloud-to-ground lightning.

Significance

Water vapor is a small but important part of the atmosphere. The density of the atmosphere is influenced by the concentration of water vapor, which in turn impacts the speed of remote sensing signals as they travel through the atmosphere to reach a receiver on the surface of the earth. The GPS signal is slowed down by a known amount, allowing Suparta to calculate the amount of water vapor in the troposphere, the lowest part of the atmosphere where weather occurs, when the signal passed through.>

This technique provides the promising beginnings of using GPS data to infer lightning events, and possibly as a warning prior to any cloud-to-ground. GPS networks such as UNAVCO’s Plate Boundary Observatory on the west coast of the North America provide an already existing infrastructure to measure atmospheric water vapor in near-continuous real-time.

Figure 3. Response of Rainfall, Pressure, Temperature, Relative Humidity and Precipitable Water Vapor (PWV) to lightning activity (CG) on 7 November 2009. The label of f, g, and h in the PWV panel show the PWV increase... Read more »